[JMcDonald]

Hello, everyone! I have been lurking for a little while. I have a pretty standard Mini Mill, with a belt drive conversion. I am in the process of beefing up the column, base, and column-base interface with about 100lb of steel for increased rigidity.

I recently purchased a 1.25" indexable end mill that has two TPG322 carbide inserts. I reasonably understand the nomenclature, but I have a couple of practical questions:

First:
TPG321 = 1/64" radius
TPG322 = 1/32" radius
TPG323 = 3/64" radius
TPG324 = 1/8" radius

As I understand it, a larger nose radius on the cutters means better finish (at a given ipm / rpm), but at the expense of greater stresses on the tool, spindle, and machine. I mostly bought and have used this cutter for facing sides, with cuts of .020 DOC max, and .001-.003 for the finish pass, with great results in AL and pretty good results in steel.

So, my first question: in my light-duty mini mill (and what Id probably call light-moderate duty after the modifications are all done), would anyone recommend stepping up to the 323 or even 324 cutters for face milling only?

Secondly, would you recommend TNG ("N" meaning "Negative Rake") over the TPG cutters for working mild steel? I used the factory TPG322 cutters on steel with pretty good results (aluminum finish was smooth as glass--this was smooth but with obvious tool marks), but would I see better results or appreciably-longer cutter life with TNG inserts?

Thanks!

[awerby]

I don't see why having a large radius on the inserts would stress your machine more; it seems that the opposite would be true. If the corners of the tool dig into the material, that's a big cause of stress; you do get better finishes with some radius, because those sharp corners aren't plowing up the steel.

You generally use negative-rake cutters for brass; I don't think you want that for cutting steel.

[rs4race]

It makes sense that the larger radius would demand more power and rigidity from your machine. You could calculate the HP requirement and cutting forces. There's going to be some point where you don't have enough power and/or rigidity to make the cut and quality will diminish.

I have had a lot of help from various parts manufactures and have heard that tool companies are the same way. I would send them an email with your questions, and I'm sure they will steer you in the right direction. They are experts on their tools. If you do make sure to share what you find out.

[109jb]

It does not make sense that more HP is required. If anything, less would be required for a larger radius, but for the radii in question it is going to be insignificant.

Think about a 1" ball nose end mill vs. a 1" square nose end mill, both cutting a full width slot at 0.5" deep. For the same feed rate, the ball nose end mill material removal rate is going to be less than the square nose end mill. Material removal rate has a direct impact on power required.

If you don't believe me then calculate it yourself at the following link

KM Indexable Torque and Power

[rs4race]

It does not make sense that more HP is required. If anything, less would be required for a larger radius, but for the radii in question it is going to be insignificant.

Think about a 1" ball nose end mill vs. a 1" square nose end mill, both cutting a full width slot at 0.5" deep. For the same feed rate, the ball nose end mill material removal rate is going to be less than the square nose end mill. Material removal rate has a direct impact on power required.

If you don't believe me then calculate it yourself at the following link

KM Indexable Torque and Power

Hmm did you attempt to use that calculator before you shared?

[109jb]

Yes. It did not make sense to me that just having a radius would increase power requirements for the reasons I stated. I verified it using the linked calculator.